In recent years, as networks have become common, documents, which were traditionally distributed in the shape of printed matters have been distributed as so-called electronic documents. Further, books, magazines and the like have been often provided as so-called electronic publishing. However, it is suggested that in terms of reading such information, traditional light emitting displays cause acute tiredness in view of human engineering and are not appropriate for long reading. Further, when the traditional light emitting display is used for a portable information terminal, continuous operating time by a battery is not sufficient in terms of power consumption, and such portable information terminal does not have sufficient usefulness to the degree that the portable information terminal can outplace paper newspaper, paper magazines and the like in terms of handling and carry. Meanwhile, reflective liquid crystal displays can be driven by low power consumption. However, the reflectance in displaying while color is 30%, which means the visibility is significantly poor compared to of paper printed matters, and therefore, the reflective liquid crystal display is not appropriate for long reading as well.
Therefore, a so-called paperlike display or an electronic paper has been developed. The display mechanism thereof is as follows. Any paperlike display sandwiches a display material between two electrode substrates and selectively display according to whether an electric field is applied to the display material or not. For example, electrophoresis for moving colored particles between the electrodes, or a method for developing the selected color by rotating dichromatic particles in an electric field are well known. However, these methods have disadvantages that the contrast is low since light is absorbed in the gap between particles, and the practical writing speed (within 1 sec) is not able to be obtained unless the driving voltage is 100 V or more. Meanwhile, an electrochromic display (ECD), which develops color based on electrochemical action has the high contrast, and therefore the ECD has been already in practical use as a light control glass and a clock/watch display. However, black color in the ECD is not high grade generally. Further, it is thinkable that there is a problem that since an organic material is used as a black material, black color is faced and the black color density is decreased with age.
Meanwhile, recently, an electrodeposition display device (EDD) for performing display by utilizing deposition and dissolution of a metal by electrochemical redox has been suggested. The display panel of the EDD is basically a cell having the internal construction as of FIG. 23. In the cross section of the cell, a transparent substrate 101 and a rear substrate 102 are oppositely arranged, and a transparent electrode 103 and an opposite electrode (common electrode) 104 are formed on the respective opposed face sides of the substrates. Further, a gelatinous electrolyte layer 105 containing metal ions such as silver ions as a display material is sandwiched between the transparent substrate 101 and the rear substrate 102.
In the display as above, color is developed by depositing the metal ions in the electrolyte layer 105 as a metal on the surface of the transparent electrode 103 by applying a given voltage to the electrodes 103 and 104, and color is extinguished by dissolving the deposited metal by applying a reverse voltage. In the EDD, the contrast and the black color density can be improved by using the foregoing display method and adding a white color pigment to the electrolyte layer.
The display panel of the EDD is manufactured by a method, in which an outer shell of the cell is formed by opposing the electrode substrates, and then a display material in a state of fluid is filled inside thereof. Specifically, vacuum injection method has been traditionally adopted. The vacuum injection method is performed as shown in FIG. 24. That is, a vacant cell 110 provided with an opening 110A on one side edge is accommodated in a chamber 130. After vacuumization is performed to the inside, the opening 110A is impregnated with a display material 131, and air is leaked in the chamber 130 to return the pressure around the cell 110 to the ambient pressure. At this time, the display material 131 is pressed by the ambient pressure, and filled inside the depressurized cell 110. This method is the most general technique in the liquid crystal injection step in manufacturing a liquid crystal panel, and is often used for manufacturing a display panel of the ECD as well.
In the case of the EDD, the cell 110 is formed, for example, as follows. First, a thick adhesive film 106 is laid along the edge of the rear substrate 102 except for the opening 110A (FIG. 25A). The adhesive film 106 is electrolytic solution-resistant, and is die-cut in the shape of a picture frame except for the opening 110A. Next, the transparent substrate 101 is further laid on the rear substrate 102, and thermocompression bonding and the like is thereto performed (FIG. 25B). Then, a void is formed between the substrates 101 and 102 by the thickness of the adhesive film 106, and the electrolytic solution is injected into the void. After the electrolytic solution is injected, when the opening 110A is sealed by a sealing member 107, the cell 110 is hermetically sealed and appearance as a display panel is formed (FIG. 26).
As above, the vacuum injection method is a technique universally applicable. However, in the past, there have been problems as follows: (1) since the liquid crystal material and the display materials such as an electrolytic solution are exposed to vacuum, low-boiling constituents are volatilized and scattered, and therefore the constituent composition is gradually altered; (2) since moisture, impurities, or air bubbles are pushed to the side edge on the other side of the opening into which the display material is injected and remain, display characteristics in the vicinity thereof become deteriorated; and (3) since depressurization is needed, necessary time for the entire injection step becomes long.
Therefore, regarding the liquid crystal panel, various filling methods have been heretofore suggested. For example, as in FIG. 27, there is a method, in which openings 111A and 111B are provided at two locations on the opposite sides of a vacant cell 111 and while injecting liquid crystal from the opening 111A at normal pressures, deaeration is performed from the opening 111B, and thereby the liquid crystal is filled (refer to Japanese Unexamined Patent Application Publication No. H07-234412). Further, as in FIG. 28, a method in which of a vacant cell 121, at least a portion except for an opening 121B is enclosed in a pressure bath 122 to which pressure is applied, and thereby a difference is made between a pressure P1 applied to an opening 121A and a pressure P2 applied to an opening 121B (P1>P2), and liquid crystal is injected from the opening 121A is disclosed (refer to Japanese Unexamined Patent Application Publication No. H09-236810). In these methods, a pressure difference between the inside and the outside of the cell can be generated without using a chamber, there is no danger of composition alteration of the liquid crystal material caused by exposure to vacuum, and the depressurization step is not necessary. Further, by performing suction and evacuation from the opening on the other side of the injection side, liquid crystal is filled into the cell more positively compared to in the vacuum injection method, and it is possible to prevent residual such as air bubbles and impurity from remaining in the cell, and prevent the concentration in the cell from being changed.
However, regarding the EDD recently developed, its electrolytic solution filling method has not been established yet, and discussion on which method is suitable has not been made. As for applying the vacuum injection method to the EDD, the following inherent problems exist. Therefore, a new method of manufacturing a panel outplacing the vacuum injection method has been aspired.
(1) Even if a small amount of the electrolytic solution is adhered around the opening, effect of the adhesive is significantly lost, and therefore sealing becomes difficult. Therefore, in the vacuum injection method in which part of the sealing material is opened and which is impregnated in the electrolytic solution, complete sealing is difficult.(2) Since an organic solvent is used for the electrolytic solution, solvent resistance of the substrate and the sealing material is strictly needed. Therefore, types of usable materials are limited.(3) When the boiling point of the electrolytic solution is not sufficiently high, or when the electrolytic solution is volatilized, decomposed, and generates corrosive gas, the inside of the chamber and the decompressor are contaminated in the vacuum injection method. Further, the electrolytic solution which is volatilized and adhered inside the unit may be dried, separated, and mixed in the solution.(4) The viscosity of the electrolytic solution is significantly high compared to of the liquid crystal. Therefore, injection takes very long time.(5) In general, it is not possible to leave for a long time the prepared electrolytic solution at room temperatures. When an electrolytic solution in which a powder material is dispersed is used, the powder material is precipitated. When an organic oxide is used as a polymerization initiator for a resin mixed in the electrolytic solution, deterioration is caused at room temperatures.(6) When an electrolytic solution in which a powder material is dispersed is used, the powder material and the electrolytic solution are separated in the cell in the process of injection.(7) When a flexible display panel is manufactured by using a film substrate and the like, filling a display material is difficult by the vacuum injection method.